1. Field of Invention
This Invention relates to controlling gap thickness of a liquid crystal electro-optical device.
2. Prior Art
FIG. 2 shows a sealing portion structure of a conventional liquid crystal electro-optical device. Glass fiber 3 are included in sealing material 2 for determining and maintaining a sealing portion gap thickness h, and liquid crystal 6 is sealed between upper and lower substrates 1 having transparent electrode films thereon.
Sealing material 2 includes glass fiber 3 of 1 wt % to sealing material, and the diameter of the glass fibers 3 is about 0.4 .mu.m bigger than the desired thickness of the sealing gap for controlling its thickness. A pressure of 0.8 kg/cm.sup.2 is applied to form the sealing portion.
However, the actual gap at the sealing portion usually becomes 0.1 .mu.m to 0.2 .mu.m narrower than the desired gap; thereby, gap the thickness difference between cell gap k and sealing portion gap h becomes about 0.2 .mu.m to 0.3 .mu.m which causes defects such as uneven tone in a liquid crystal electro-optical display.
If the desired gap thickness is 7.0 .mu.m, 1 wt % of 7.4 .mu.m glass fibers should be included in the sealing material and a pressure of 0.8 kg/cm.sup.2 is required to seal the substrates; however, actual cell gap thickness results 6.8 .mu.m to 6.9 .mu.m.
Problems to be solved by the Invention
Super Twisted Nematic mode is mostly used for a liquid crystal electro-optical device because of its superiority of electro-optical characteristics. Uniformity of cell gap thickness is one of the most important qualities required for a liquid crystal cell.
As FIG. 2 shows, cell gap thickness means the gap distance between upper and lower glass substrates and the gap is held by having spacers 5 in display area and glass fibers 3 included in the sealing material 2. Uniformity required for cell gap thickness should be within .+-.0.1 .mu.m. Without this cell gap uniformity, problems are caused, such as irregular tone or bad contrast in liquid crystal electro-optical devices.
As FIG. 2 shows, gap difference exists between cell gap thickness k and sealing portion gap thickness h. This difference causes is created at the time of crimping, and the sealing portion gap thickness becomes 0.1 .mu.m to 0.2 .mu.m smaller than the desired gap thickness. Even if bigger particles of glass fiber are used, cell gap thickness is still uneven or worse, which makes color tone differences greater between the tone of the display area and that of the margin area. It was is very difficult to hold the whole cell gap uniform.